<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .content{
            height: 3000px;
            border: 1px solid #000;
        }
        .box{
            position: fixed;
            bottom: 100px;
            right: 100px;

            width: 100px;
            height: 100px;
            line-height: 100px;
            text-align: center;
            border: 1px solid red;
            border-radius: 5px;

        }
    </style>
</head>
<body>
    <div class="box">
        意见反馈
    </div>
    <div class="content">

    </div>
</body>
</html>